Environmentally preferable method of making solid electrolyte and integration of metal anodes thereof

ABSTRACT

A novel and environmentally preferable method is provided for preparing solid electrolyte particles capable of making dense, flexible, Li+ conducting electrolyte thin films. Methods are also provided for using the solid electrolyte particles and/or thin films in manufacturing safer and more efficient lithium-based batteries. In particular, the method uses inorganic precursors instead of using organic precursors in preparing an aerosol and then convert the aerosol to solid powders to provide the solid electrolyte particles. The solid electrolyte particles prepared have a cubic polymorph and have a desired particle size range, and are capable of making a solid electrolyte film with a thickness less than 50 μm.

TECHNICAL FIELD

This disclosure relates to a novel and environmentally preferable methodof preparing solid electrolyte particles capable of making dense,flexible, Li⁺ conducting electrolyte thin films, and methods of usingthe solid electrolyte particles and/or thin films in manufacturing saferand more efficient lithium-based batteries.

TECHNICAL BACKGROUND

Because lithium batteries have great electrochemical capacity, highoperating potential and superior charge/discharge cycles, demandtherefor in the fields of portable information terminals, portableelectronic devices, small power storage devices for home use,motorcycles, electric cars, hybrid electric cars, and the like isincreasing. Hence, improvements to the safety and performance of lithiumbattery are required in response to the proliferation of suchapplications.

Conventional lithium batteries using a liquid electrolyte areproblematic because of possible leakage and easy ignition of theelectrolyte. Such problems pertaining to safety come to the fore aselectric cars are becoming popular.

In order to improve safety, thorough research is thus ongoing these daysinto all-solid-state batteries using a solid electrolyte composed of anon-combustible inorganic material. All-solid-state batteries, havingstability, high energy density, potentially simple manufacturingprocesses, large/small sizes, and low prices, are receiving attention asa next-generation battery.

SUMMARY

This disclosure relates to a novel and environmentally preferable methodof preparing solid electrolyte particles capable of making dense,flexible, Li⁺ conducting electrolyte thin films, and methods of usingthe solid electrolyte particles and/or films in manufacturing safer andmore efficient lithium-based batteries. Particularly, the new methoduses flame-assisted spray pyrolysis to covert inorganic precursors tomake desirable cubic Li₇La₃Zr₂O₁₂ (c-LLZO) based particles that arecapable of making thin c-LLZO based films suitable for solid-statelithium batteries.

In a first aspect, the present disclosure provides a method of preparingsolid electrolyte particles. The method may include: preparing asolution of solid electrolyte precursors by dissolving a mixturecomprising an inorganic lithium precursor, an inorganic lanthanumprecursor, and an inorganic zirconium precursor in an organic solvent;generating an aerosol of said solution; converting the aerosol to solidpowders at elevated temperature; and annealing said solid powders toprovide the solid electrolyte particles. The solid electrolyte particleshave a cubic polymorph and have a particle size range of about 20 nm to10 μm, and the solid electrolyte particles are capable of making a solidelectrolyte film with a thickness between about 5-50 μm.

In a second aspect, the present disclosure provides method of using thesolid electrolyte particles to make thin films with a thickness of about5-50 μm.

In a third aspect, the present disclosure provides method of using thethin films with a thickness of about 5-50 μm to make safer andsolid-sate lithium batteries.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the Field Emission Scanning Electron Microscopy (FESEM)image of LLZO particles of Example 1 with a magnification factor of16,000.

FIG. 2 shows the FESEM image of LLZO particles of Example 1 with amagnification factor of 33,000.

FIG. 3 shows the X-Ray Diffraction (XRD) of LLZO particles of Example 1.

DETAILED DESCRIPTION

A solid-state battery is configured to include a cathode, a solidelectrolyte layer and an anode, in which the solid electrolyte of thesolid electrolyte layer has to possess high ionic conductivity and lowelectronic conductivity. It can be configured as all-solid-statebatteries with no liquid or semi-solid-state batteries with smallportion of liquid. Furthermore, for all-solid-state batteries, a solidelectrolyte can be contained in the cathode and the anode as electrodelayers.

A solid electrolyte that satisfies the requirements of the solidelectrolyte layer of the solid-state secondary battery includes asulfide, an oxide, a solid polymer or the like. In particular, asulfide-based solid electrolyte is problematic in terms of production ofa resistance component through the interfacial reaction with a cathodeactive material or an anode active material, high moisture absorptionproperties, and also generation of a hydrogen sulfide (H₂S) gas that ispoisonous.

Immense attention and effort have been given to cubic Li₇La₃Zr₂O₁₂(c-LLZO) or other metal doped c-LLZO as it exhibits a combination ofdesirable characteristics such as high ionic conductivities (0.1-1mS/cm), lithium stability, wide electrochemical operating window (˜6 V)and pH stability (7-11.5). In particular, due to higher safety standardsrequired for bulk battery systems, recent interest has grown inincorporating c-LLZO in all-solid-sate lithium batteries (ASLBs) toconstruct inherently safe cells, concomitantly obviating safetymechanisms related to lithium ion batteries.

There is considerable need today for c-LLZO electrolyte films less than50 μm thick. Despite the need and interest, most prototype cells userelatively thick LLZO membrane (50-200 μm or even 1 cm) that areproduced by LLZO powders (normally with unevenly distributed particlesizes of about ten to several hundred μm) from solid-state chemicalreactions along with high temperature sintering. Net ionicconductivities at this thickness are far from optimal and reduce thepotential utility in lithium batteries for bulk storage applications.

In order for c-LLZO to be used in actual cells, it must be incorporatedin thin film forms preferably less than 50 μm. However, very few dense,thin c-LLZO films with ionic conductivities equivalent to those found inhigh density, bulk counterparts (over 0.1 mS/cm) have been reportedlikely due to the energy intensive and rather problematic sinteringprocesses. Normal sintering conditions are 1100-1250° C. for 10-40hours. Under such harsh conditions, lithium (as Li₂O) volatizes rapidlyat these temperatures presenting exceptional challenges in producingthin films giving much higher surface/volume ratios leading to fasterlithium loss.

Yi et al. disclosed a method of using organic precursors to preparec-LLZO that is capable of making thinner c-LLZO films. However, it maynot economically or environmental preferable in industrial scale up byusing organic precursors. See Yi et al., Flame made nanoparticles permitprocessing of dense, flexible, Li⁺ conducting ceramic electrolyte thinfilms of cubic-Li₇La₃Zr₂O₁₂ (c-LLZO), J. Mater. Chem. A, 2016, 4,12947-12954.

Therefore, there is still a need to develop a more economically andenvironmentally preferable method for preparing c-LLZO particles thatare capable of making thin c-LLZO films suitable for solid-sate lithiumbatteries.

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the examplesillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of this disclosure is thereby intended.

In the present disclosure the term “about” can allow for a degree ofvariability in a value or range, for example, within 20%, within 10%,within 5%, or within 1% of a stated value or of a stated limit of arange.

Generally, c-LLZO particles are prepared by solid state reactions. Itmeans that solid state inorganic precursors are reacted under very hightemperature, which is usually over 1000° C. Such solid state reactionoften needs significantly amount of energy. In addition, the particlesobtained do not have good quality due to larger particle sizes and/ornot uniform particle shapes as well as incomplete reactions. Such kindof particles are not able to provide high quality and thin films thatare required for solid state electrolyte lithium-based batteries.

Yi et al. reported using organic precursors to prepare higher qualityc-LLZO particles. See Yi et al., Flame made nanoparticles permitprocessing of dense, flexible, Li⁺ conducting ceramic electrolyte thinfilms of cubic-Li₇La₃Zr₂O₁₂ (c-LLZO), J. Mater. Chem. A, 2016, 4,12947-12954. However, each precursor has to be prepared as an organiccompound. It is also expensive and less favorable than more readilyavailable solid precursor such as salt or oxide.

Inorganic salts normally dissolve in water instead of organic solvent.The aqueous precursor may not provide comparable quality c-LLZOparticles and may need higher temperature. The present disclosure foundsome organic solvent can dissolve some inorganic precursors. Suchorganic solution can go through aerosol and react at elevatedtemperature to provide good quality c-LLZO or doped c-LLZO particles,which can be converted to suitable thin films for lithium-basedbatteries. Such method is therefore more economically andenvironmentally favorable for industrial scale-up.

In the present disclosure the term “substantially” can allow for adegree of variability in a value or range, for example, within 80%,within 85%, within 90%, within 95%, or within 99% of a stated value orof a stated limit of a range.

In the present disclosure the term “aerosol” refers to a suspension offine solid particles or liquid droplets, in air or another gas or gasmixture. The gas mixture may be a mixture of oxygen, nitrogen, anorganic solvent such as methanol or ethanol. In one aspect, the term“aerosol” refers to liquid solution droplets.

In one example, the present disclosure provides a method of preparingsolid electrolyte particles, wherein the method comprises:

-   -   a) preparing a solution of solid electrolyte precursors by        dissolving a mixture comprising an inorganic lithium precursor,        an inorganic lanthanum precursor, and an inorganic zirconium        precursor in an organic solvent;    -   b) generating an aerosol of said solution;    -   c) converting the aerosol to solid powders at elevated        temperature; and    -   d) annealing said solid powders to provide the solid electrolyte        particles, wherein the solid electrolyte particles have a cubic        polymorph and have a particle size range of 20 nm to 10 μm, and        the solid electrolyte particles are capable of making a solid        electrolyte film with a thickness between about 5-50 μm.

In one example, the present disclosure provides a method of preparingsolid electrolyte particles, wherein the method comprises:

-   -   a) preparing a solution of solid electrolyte precursors by        dissolving a mixture comprising an inorganic lithium precursor,        an inorganic lanthanum precursor, and an inorganic zirconium        precursor in an organic solvent, wherein said mixture may        further comprise an optional inorganic yttrium precursor, an        optional inorganic niobium precursor, an inorganic germanium        precursor, or an optional inorganic aluminum precursor;    -   b) generating an aerosol of said solution;    -   c) converting the aerosol to solid powders at elevated        temperature; and    -   d) annealing said solid powders to provide the solid electrolyte        particles, wherein the solid electrolyte particles have a cubic        polymorph and have a particle size range of 20 nm to 10 μm, and        the solid electrolyte particles are capable of making a solid        electrolyte film with a thickness between about 5-50 μm.

In any example of the present disclosure, the prepared solution ofinorganic precursors is a substantially homogeneous solution in organicsolvent or organic solvent mixture.

In any example of the present disclosure, an organic solvent used toprepare inorganic precursor solution may be any polar organic solventsuch as an alcohol, carboxylic acid, ester, ether, or any combinationthereof. In one aspect, the solvent may be a C₁-C₆ straight, branched orcyclic alcohol, or any combination thereof. The preferred alcohol ismethanol or ethanol. In one aspect, the solvent may be a C₂-C₆ straight,branched or cyclic carboxylic acid, or any combination thereof. Thepreferred carboxylic acid is acetic acid.

In any example of the present disclosure, an inorganic lithium precursormay be any lithium salt, which may be but is not limited to a nitrate,sulfate, chloride, fluoride, bromide, hydroxide, carbonate, bicarbonate,phosphate, dihydrogen phosphate, hydrogen phosphate, acetate, oxalate,any hydrate thereof, or any combination thereof. A preferred lithiumprecursor is lithium nitrate or a hydrate thereof.

In any example of the present disclosure, an inorganic lanthanumprecursor may be any lanthanum salt, which may be but is not limited toa nitrate, sulfate, chloride, fluoride, bromide, hydroxide, carbonate,bicarbonate, phosphate, dihydrogen phosphate, hydrogen phosphate,acetate, oxalate, any hydrate thereof, or any combination thereof. Apreferred lanthanum precursor is lanthanum nitrate or a hydrate thereof.

In any example of the present disclosure, an inorganic zirconiumprecursor may be any zirconium salt, which may be but is not limited toa nitrate, sulfate, chloride, fluoride, bromide, hydroxide, carbonate,bicarbonate, phosphate, dihydrogen phosphate, hydrogen phosphate,acetate, oxalate, any hydrate thereof, or any combination thereof. Apreferred zirconium precursor is zirconium nitrate or a hydrate thereof.

In any example of the present disclosure, an optional inorganic yttriumprecursor may be any yttrium salt, which may be but is not limited to anitrate, sulfate, chloride, fluoride, bromide, hydroxide, carbonate,bicarbonate, phosphate, dihydrogen phosphate, hydrogen phosphate,acetate, oxalate, any hydrate thereof, or any combination thereof. Apreferred yttrium precursor is yttrium nitrate or a hydrate thereof.

In any example of the present disclosure, an optional inorganic niobiumprecursor may be any niobium salt, which may be but is not limited to anitrate, sulfate, chloride, fluoride, bromide, hydroxide, carbonate,bicarbonate, phosphate, dihydrogen phosphate, hydrogen phosphate,acetate, oxalate, any hydrate thereof, or any combination thereof. Apreferred niobium precursor is niobium nitrate or oxalate, or a hydratethereof. In one aspect, the inorganic niobium precursor is ammoniumniobate (V) oxalate or a hydrate thereof.

In any example of the present disclosure, an optional inorganicgermanium precursor may be any germanium salt, which may be but is notlimited to a nitrate, sulfate, chloride, fluoride, bromide, hydroxide,carbonate, bicarbonate, phosphate, dihydrogen phosphate, hydrogenphosphate, acetate, oxalate, any hydrate thereof, or any combinationthereof. A preferred germanium precursor is germanium nitrate or ahydrate thereof.

In any example of the present disclosure, an optional inorganic aluminumprecursor may be any aluminum salt, which may be but is not limited to anitrate, sulfate, chloride, fluoride, bromide, hydroxide, carbonate,bicarbonate, phosphate, dihydrogen phosphate, hydrogen phosphate,acetate, oxalate, any hydrate thereof, or any combination thereof. Apreferred aluminum precursor is aluminum nitrate or a hydrate thereof.In one aspect, the aluminum precursor is added to stabilize the cubicpolymorph of c-LLZO.

In one aspect, an optional second inorganic lithium material may beadded to an inorganic precursor mixture to make an inorganic precursorsolution to compensate the possible loss of lithium during theconversion of the aerosol to said solid powders at elevated temperature.The optional second inorganic lithium material may be the same ordifferent from the lithium precursor. The optional second inorganiclithium material may be any lithium oxide or lithium salt. The lithiumsalt may be but is not limited to a nitrate, sulfate, chloride,fluoride, bromide, hydroxide, carbonate, bicarbonate, phosphate,dihydrogen phosphate, hydrogen phosphate, acetate, oxalate, any hydratethereof, or any combination thereof. In one aspect, about 5-50 wt %,5-40%, 5-30%, 5-20%, 10-50%, 10-40%, 10-30%, or 10-20% excess of secondinorganic lithium material may be added to compensate for lithium lossduring the conversion of aerosol to solid powders at elevatedtemperature and/or during the annealing process. A preferred optionalsecond inorganic lithium material is lithium carbonate, lithium oxide, ahydrate thereof, or any combination thereof.

In one example, the present disclosure provides a method of preparingsolid electrolyte particles. The method may include:

-   -   a) preparing a solution of solid electrolyte precursors by        dissolving a mixture comprising an inorganic lithium precursor,        an inorganic lanthanum precursor, and an inorganic zirconium        precursor in an organic solvent, wherein said mixture may        further comprise an optional inorganic yttrium precursor, an        optional inorganic niobium precursor, an inorganic germanium        precursor, or an optional inorganic aluminum precursor;    -   b) generating an aerosol of said solution;    -   c) converting the aerosol to solid powders at elevated        temperature; and    -   d) annealing said solid powders to provide the solid electrolyte        particles.

The solid electrolyte particles have a cubic polymorph and have aparticle size range of 20 nm to 10 μm, and the solid electrolyteparticles are capable of making a solid electrolyte film with athickness between about 5-50 μm.

The inorganic lithium precursor is lithium nitrate, hydrate thereof, orany combination thereof the inorganic lanthanum precursor is lanthanumnitrate, hydrate thereof, or any combination thereof; the inorganiczirconium precursor is zirconium nitrate, hydrate thereof, or anycombination thereof; the optional inorganic yttrium precursor is yttriumnitrate, hydrate thereof, or any combination thereof, optional inorganicniobium precursor is ammonium niobate (V) oxalate or a hydrate thereofthe optional inorganic germanium precursor is germanium nitrate, hydratethereof, or any combination thereof, and the optional inorganic aluminumprecursor is aluminum nitrate, hydrate thereof, or any combinationthereof.

In any example, the ratio of inorganic precursors to make the solidelectrolyte particles is adjusted to ensure the solid electrolyteparticles be represented by formula Li₇La₃Zr₂O₁₂,Li_(7-3x)Al_(x)La₃Zr₂O₁₂, Li_(7-3x)Y_(x)La₃Zr₂O₁₂,Li_(7-3x)Nb_(x)La₃Zr₂O₁₂, Li_(7-3x)Ga_(x)La₃Zr₂O₁₂, or any combinationthereof, wherein 0≤x≤2. In one aspect, the total lithium molar ratio ofthe required inorganic lithium precursor:the total lanthanum molar ratioof the inorganic lanthanum precursor:the total zirconium molar ratio ofthe inorganic zirconium precursor is about 5-9:0.5-3.5:0.5-2.5. In oneaspect, the total lithium molar ratio of inorganic lithium precursor:thetotal lanthanum molar ratio of the inorganic lanthanum precursor:thetotal zirconium molar ratio of inorganic zirconium precursor is about7:3:2. In one aspect, when an optional inorganic aluminum precursor isadded, the molar ratio of the optional inorganic aluminum precursor tothe inorganic lanthanum precursor is about 1:20, 1:15, 1:10, or 1:5. Inone preferred aspect, the molar ratio of the optional inorganic aluminumprecursor to the inorganic lanthanum precursor is about 1:10. In oneaspect, when an optional inorganic yttrium precursor is added, the molarratio of the optional inorganic yttrium precursor to the inorganiclanthanum precursor is about 1:200, 1:175, 1:150, 1:125, 1:100, 1:90,1:80, 1:70, 1:60, or 1:50. In one preferred aspect, the molar ratio ofthe optional inorganic yttrium precursor to the inorganic lanthanumprecursor is about 1:100. In one aspect, when an optional inorganicniobium precursor is added, the molar ratio of the optional inorganicniobium precursor to the inorganic lanthanum precursor is about 1:20,1:15, 1:10, or 1:5. In one preferred aspect, the molar ratio of theoptional inorganic niobium precursor to the inorganic lanthanumprecursor is about 1:10.

In one example, the aerosol of the inorganic precursor solution may begenerated by any aerosol generator such as an atomizer. Any suitable gasor gas mixture can be used as atomizing gas. In one aspect, the aerosolmay be generated by an atomizer with methanol-saturated nitrogen asatomizing gas. In one aspect, the flow rate of H₂ and the atomizing gasare kept at a substantially constant rate, respectively. The flow rateof H₂ and the atomizing gas may be same or different.

In one example, the step of converting an aerosol to solid powders atelevated temperature may be achieved by method such as but is notlimited to flame-assisted spray pyrolysis, ultrasonic spray pyrolysis,sol-gel process, electrospinning, or any combination thereof. In oneaspect, the method is flame-assisted spray pyrolysis.

In one example, the methods of making c-LLZO solid electrolyte particlesprovides improved particle size range and/or particle shape. The methodof the present disclosure can provide average smaller particle sizessuch as nanometer or micrometer diameter particles. The method of thepresent disclosure may avoid using the high energy ball milling process,which can add significant cost. In one aspect, the average particle sizerange of the solid electrolyte particles is about 20 nm to 10 μm, 20 nmto 5 μm, 20 nm to 4 μm, 20 nm to 3 μm, 20 nm to 2 μm, 20 nm to 1 μm, 20nm to 0.9 μm, 20 nm to 0.8 μm, 20 nm to 0.7 μm, 20 nm to 0.6 μm, 20 nmto 0.5 μm, 20 nm to 0.4 μm, 20 nm to 0.3 μm, 20 nm to 0.2 μm, 20 nm to0.1 μm, 50 nm to 10 μm, 50 nm to 5 μm, 50 nm to 4 μm, 50 nm to 3 μm, 50nm to 2 μm, 50 nm to 1 μm, 50 nm to 0.9 μm, 50 nm to 0.8 μm, 50 nm to0.7 μm, 50 nm to 0.6 μm, 50 nm to 0.5 μm, 50 nm to 0.4 μm, 50 nm to 0.3μm, 50 nm to 0.2 μm, 50 nm to 0.1 μm, 100 nm to 10 μm, 100 nm to 5 μm,100 nm to 4 μm, 100 nm to 3 μm, 100 nm to 2 μm, 100 nm to 1 μm, 100 nmto 0.9 μm, 100 nm to 0.8 μm, 100 nm to 0.7 μm, 100 nm to 0.6 μm, 100 nmto 0.5 μm, 100 nm to 0.4 μm, 100 nm to 0.3 μm, 100 nm to 0.2 μm, 500 nmto 10 μm, 500 nm to 5 μm, 500 nm to 4 μm, 500 nm to 3 μm, 500 nm to 2μm, 500 nm to 1 μm, or any combination thereof.

In one example, the temperature of annealing solid powders obtained fromthe converting of aerosol is about 500-1200° C., 600-1200° C., 700-1200°C., 500-1000° C., 600-1000° C., 700-1000° C., 500-800° C., 600-800° C.,or 700-800° C. In one aspect, the annealing temperature is about 700° C.In one aspect, the annealing time is about 0.5-6 h, 0.5-5 h, 0.5-4 h,0.5-3 h, 01-6 h, 1-5 h, 1-4h, or 1-3 h.

The present disclosure also provides method to make c-LLZO basedsolid-state electrolyte film/membrane. Solid electrolyte particles ofthe present disclosure may be combined with additives/solvents such asgelatin, butadiene or polybutadiene, acrylonitrile or polyacrylonitrile,polyvinyl butyral, benzyl butyl phthalate, acetone, and/or ethanol toform a suspension, which can be casted with a suitable coater such aswire wound rod coater to fabricate c-LLZO based solid-state electrolytefilm/membrane with a thickness of about less than 50 μm, less than 45μm, less than 40 μm, less than 35 μm, less than 30 μm, less than 25 μm,or less than 20 μm. In one aspect, the thickness of the film/membrane isabout 5-50 μm, 5-45 μm, 5-40 μm, 5-35 μm, 5-30 μm, 5-25 μm, or 5-20 μm.

In one example, the c-LLZO based solid-state electrolyte film/membraneof the present disclosure may be paired with lithium metal in lithiumbattery manufacturing. By using atomic layer deposition method, anultra-thin layer of metal oxide such as but is not limited to La₂O₃,CuO, ZrO₂, HfO₂, or any combination thereof may be deposited on c-LLZObased solid-state electrolyte film/membrane to form a metal oxide layer,and followed by physically and chemically integrating lithium metal ontothe metal oxide layer. The thickness of the metal oxide layer is about0.5-20 nm, 0.5-15 nm, 0.5-10 nm, 0.5-5 nm, 1-20 nm, 1-15 nm, 1-10 nm, or1-5 nm. Alternatively, the c-LLZO based solid-state electrolytefilm/membrane may be treated with argon, nitrogen, oxygen, or othersuitable gas plasma for a short period of time such as about 10-60seconds, 20-45 second, or 25-35 seconds. And then integrate lithiummetal on top of the c-LLZO based solid-state electrolyte film/membranewithout metal oxide layer. In either situation, the thickness of thelithium metal can be controlled within 5-50 μm with a film adaptor. Thisapproach can provide the combination of an anode and the solid-stateelectrolyte of the present disclosure.

Example 1: c-LLZO PARTICLES

A precursor solution was prepared by dissolving stoichiometricquantities (about 7:3:2 molar ratio) of LiNO₃, La(NO₃)₂ andZr(NO₃)₄.5H₂O in methanol. Al(NO₃)₃ (the molar ratio of Al:La is about0.09:1) was added to stabilize the cubic polymorph and about 10 wt %excess Li₂CO₃ was added to compensate for Li loss during calcination.Y(NO₃)₃ (the molar ratio of Y:La is 0.01:1) or Ammonium niobate(V)oxalate hydrate (the molar ratio of Nb:La is 0.1:1). The concentrationof LiNO₃ was kept about 0.5 mol/L. A precursor aerosol was generatedwith the precursor solution in an atomizer with methanol-saturated N₂atomizing gas. The atomizing gas was saturated with methanol vapor priorto entering the atomizer to prevent evaporation of solvent methanol,thus maintaining a constant precursor concentration. The flow rates ofH₂ and the atomizing gas N₂ were kept at about 0.5 L/min and 2.5 L/min,respectively. To improve the grain sizes and remove impurity phases, theflame-synthesized powder was annealed at 700° C. for 3 h to provideExample 1. FIG. 1 and FIG. 2 show the Field Emission Scanning ElectronMicroscopy (FESEM) images of the obtained LLZO particles of Example 1with magnification factor of 16,000 and 33,000, respectively. It can befound in the images that the particles size of Example 1 is in the rangeof about 50-200 nm. The FESEM images clearly show that the LLZOparticles of Example 1 are substantially spherical and uniform. Suchsubstantially spherical and uniform shaped particles make it possible toprepare thin LLZO films with a film thickness below 50 μm. FIG. 3 showsthe X-Ray Diffraction (XRD) of the obtained LLZO particles of Example 1.For the sample preparation of the Field Emission Scanning ElectronMicroscope (FESEM) characterization, LLZO powders were attached onto acarbon tape followed by gold coating to increase the conductivity. TheXRD data of Example 1 were collected in the 2-theta range from 10-50degree using Bruker X2 with CuKα radiation.

Example 2: c-LLZO FILM

As-produced powders were first dispersed in EtOH (200 proof) with about2 wt % polyacrylic acid as dispersant, and treated with an ultrasonichorn at 100 W for 15 min. The suspension was let settle for 4 hours toallow larger particles to settle. Supernatant was decanted and therecovered powder dried. Collected powder, polyvinyl butyral, benzylbutyl phthalate, acetone, and ethanol were ball-milled with sphericalZrO₂ beads for 12 h to homogenize the suspension. Suspensions were castusing a wire wound rod coater. 10-35 μm film thicknesses were controlledby adjusting the gap between the rod and the substrate. The films weremanually peeled off the Mylar substrate, and cut to selected sizes. Thefilms were uniaxially pressed in between stainless steel dies at 80-100°C. with a pressure of 50-70 MPa for 5-10 minutes using a heated benchtop press to improve packing density. The final obtained film has athickness of 22 μm. The method of preparing the film is similar to themethod of Yi et al., Flame made nanoparticles permit processing ofdense, flexible, Li+ conducting ceramic electrolyte thin films ofcubic-Li₇La₃Zr₂O₁₂ (c-LLZO), J. Mater. Chem. A, 2016,4,12947-12954.

We claim:
 1. A method of preparing solid electrolyte particles, whereinthe method comprises: a) Preparing an organic solution of solidelectrolyte precursors by dissolving a mixture comprising an inorganiclithium precursor, an inorganic lanthanum precursor, and an inorganiczirconium precursor in an organic solvent; b) generating an aerosol ofsaid organic solution; c) converting the aerosol to solid powders at anelevated temperature; and d) annealing said solid powders to provide thesolid electrolyte particles, wherein the solid electrolyte particleshave a cubic polymorph and have a particle size range of 20 nm to 10 μm,and the solid electrolyte particles are capable of making a solidelectrolyte film with a thickness between 5-50 μm.
 2. The method ofclaim 1, wherein the mixture further comprises an optional inorganicyttrium precursor, an optional inorganic niobium precursor, an optionalinorganic germanium precursor, an optional inorganic aluminum precursor,or any combination thereof.
 3. The method of claim 2, wherein the ratioof inorganic precursors to make the solid electrolyte particles isadjusted to ensure the solid electrolyte particles be represented byformula Li₇La₃Zr₂O₁₂, Li_(z-3x)Al_(x)La₃Zr₂O₁₂, Li_(z-3x)Y_(x)La₃Zr₂O₁₂,Li_(z-3x)Nb_(x)La₃Zr₂O₁₂, Li_(7-3x)Ga_(x)La₃Zr₂O₁₂, or any combinationthereof, wherein 0≤x≤2.
 4. The method of claim 2, wherein the inorganiclithium precursor is lithium nitrate, hydrate thereof, or anycombination thereof; the inorganic lanthanum precursor is lanthanumnitrate, hydrate thereof, or any combination thereof; the inorganiczirconium precursor is zirconium nitrate, hydrate thereof, or anycombination thereof; the optional inorganic yttrium precursor is yttriumnitrate, hydrate thereof, or any combination thereof; the optionalinorganic niobium precursor is niobium nitrate or oxalate or a hydratethereof; the optional inorganic germanium precursor is germaniumnitrate, hydrate thereof, or any combination thereof, and the optionalinorganic aluminum precursor is aluminum nitrate, hydrate thereof, orany combination thereof.
 5. The method of claim 1, wherein the solutionis a substantially at least 80% homogeneous solution in the organicsolvent.
 6. The method of claim 1, wherein the mixture further comprisesan inorganic lithium material to compensate the possible loss of lithiumduring the conversion of the aerosol to said solid powders at theelevated temperature, wherein the inorganic lithium material may be thesame as or different from the inorganic lithium precursor.
 7. The methodof claim 1, wherein the organic solvent comprises a polar organicsolvent.
 8. The method of claim 1, wherein the organic solvent comprisesan alcohol, carboxylic acid, ester, ether, or any combination thereof.9. The method of claim 1, wherein the organic solvent comprises methanolor acetic acid, or any combination thereof.
 10. The method of claim 6,wherein each inorganic precursor or lithium material is a nitrate,sulfate, chloride, fluoride, bromide, hydroxide, phosphate, dihydrogenphosphate, hydrogen phosphate, any hydrate thereof, or any combinationthereof.
 11. The method of claim 1, wherein the solid electrolyteparticles have a particle size range of 100 nm to 3000 nm.
 12. Themethod of claim 1, wherein the solid electrolyte particles are furtherconverted to solid electrolyte film with a thickness of 5-20 μm.
 13. Themethod of claim 1, wherein the step of converting the aerosol to solidpowders at the elevated temperature to said electrolyte material isachieved by flame-assisted spray pyrolysis, ultrasonic spray pyrolysis,sol-gel process, electrospinning, or any combination thereof.
 14. Themethod of claim 1, wherein the solid electrolyte particles are combinedwith an additive comprising gelatin, butadiene or polybutadiene,acrylonitrile or polyacrylonitrile to provide the solid electrolyte filmwith more flexibility.
 15. The method of claim 1, wherein the step ofannealing said solid powders is at a temperature of 500-800° C.
 16. Themethod of claim 1, wherein the step of annealing said solid powders isat a temperature of about 700° C.
 17. The method of claim 1, wherein theaerosol is generated with nitrogen.
 18. The method of claim 1, whereinthe organic solvent is methanol, and the aerosol is generated withmethanol-saturated nitrogen.
 19. The method of claim 1, wherein the stepof converting the aerosol to solid powders at the elevated temperatureto said electrolyte material is achieved by flame-assisted spraypyrolysis.